mmg_233_2013_genetics_genomicswikiaorg-20200214-history
Impact of Horizontal Gene Transfer on Plant Colonization
Horizontal gene transfer is a movement of genes between species. Horizontal gene transfer (HGT) is helpful to organisms because it introduces genetic novelties which can lead to an adaptation to new environments or allows access to new resources. Plant colonization About 490 million years ago the land plant emerged from charophycean green algae. These land plants then gradually evolved phenotypic novelties that allowed them to adapt to terrestrial environments. It was unsure if this was an act of HGT in land plants or not. There have been few studies showing HGT in land plants related to nuclear genes. Yue et al. plan to present evidence that HGT of nuclear genes did occur on land plant colonization. They will use the moss Physcomitrella patens, which is an extant representative of early land plants, to prove their theory. This study focused on genes in land plants that were acquired independently from other sources, using a phylogenomic analysis of the moss P. patens. They focused on identifying genes acquired from prokaryotes, viruses, and fungi. Yue et al. also decided to only identify genes in ''P.patens '' that were acquired after the separation of green plants from reg algae and glaucophytes. Results Using a program called AlienG the protein sequences of ''P. patens '' were annotated and 910 genes were identifeid as potential prokaryotic, fungal or viral origin. They removed the genes that were located on short scaffolds or high percent-identities with cyanobacterial sequences. 516 genes remained. 32 genes of four families had identifiable homologues only in prokaryotes or fungi, while 96 genes of 53 families showing a monophyletic relationship between sequences of green plants and those from prokaryote, fungi or viruses in phylogenetic analyses. In the end, 128 genes of 57 families were identified as genes derived from prokaryotes, fungi or viruses. 25 of these gene families contain mulitple copies of '' P. patens, ''which is expected for land plants who have undergone frequent duplication events. In some cases, for instance that gene family encoding FAD-linked oxidase, both acquired genes and endogenous homologues co-exist in ''P. patens. ''Two of three of the identifiable copies of ''P. patens ''that was found in the gene family encoding FAD-linked oxidase are closely related to CFB bacterial homolgues. The third identifiable copy may have been vertically inherited in eukaryotes. In the gene encoding for PEPCase two PEPcase gene copies exist in ''P. patens ''and one of them is clearly related to proteobacterial sequences, and the other is related to photosynthetic eukaryotes, the chytrid fungus ''Spizellomyces ''and other bacteria. Many of the genes identified in the analysis are related to essential or plant-specific metabolic and developmental processes. It was found that gene families related to carbohydrate metabolism were acquired from bacteria, and they are involved in starch biosynthesis, cellulose degradation, pollen and seed germination. In the subtilase gene family (Figure 1b) they were only able to identify homologues in bacteria and other land plants. This proves previous reports stating that plant subtilases differe significantly from those of fungi and animals. These land plant subtilases are derived from a single HGT event from bacteria then rapid gene duplication occurs. Other genes were identified that relate to biosynthesis of plant polyamines and hormones. A major precursor for the biosynthesis of polyamines is the ornithine. The gene that encodes arginase is responsible for degrading arginine into ornithine. This study found that the sequences of the land plant arginase shares 32-48% identities with bacterial agmatinase, however it only shares 25-28% identity with arginase from other organisms. They then used phylogenetic analyses to indicate that the land plant arginase evolved from bacterial argatinase. Other gene familes were identified in the analyses that are related to pant defence and stress tolerance. For example glutathione, which is essential for plant disease resistance. Glutamate- cysteine ligase (GCL) is one ofthe enzymes that catalyzes the formation of glutathione. This study found that ''P. patens '' GCL are only present in green plants and bacteria. The phylogenetic analyses that were used also indicated that the GCL gene was orginially acquired from bacteria. References Nature